AD NUMBER: 2012-09-02

SUMMARY: This AD was prompted by analysis that in a specific failure case of the upper primary attachment of the trimmable horizontal stabilizer actuator (THSA), the THSA upper secondary attachment engaged because it could only withstand the loads for a limited period of time. This AD requires installing three secondary retention plates for the gimbal bearings on the THSA upper primary attachment. The FAA is issuing this AD to prevent failure of the secondary load path, which could result in loss of control of the airplane.